Positronium is composed of an electron and a positron mutually orbiting each other.

It is formed when a positron is accelerated into matter and then captured by an electron.

Parapositronium is formed when the spins of the positron and electron are oppositely directed. This is the orientation of two particles orbiting each other and their magnetic fields connect like a loop that goes from one to the other.

Parapositronium annihilates into two photons, with a mean life of about one-tenth of a nanosecond (or 10-10 second; a nanosecond is 10−9 second).

Orthopositronium is composed of an electron and positron which are mutually orbiting each other, but their spins are in the same direction. This means that the magnetic field orientation of the two particles is across the orbit. In other words, the North-South pole of the electron may point toward the center of the orbit, and the pole of the positron may point away from the center of the orbit (i.e. its South pole aimed at the orbital center).

Orthopositronium annihilates into three photons with a mean life of about 100 nanoseconds (10-7 second). This system collapses into 3 photons because the energy of the system requires that 2 photons be formed to conserve the energy of the mass and kinetic energy of rotation, and the 3rd photon carries the energy associated with the rotation of the magnetic pole of the system.